1. Field of the Invention
The invention is directed to radar devices, and more particularly to (1) special circuits for use in modulated CW or pulse Doppler radar for enabling the radar to distinguish not only the phase differences (Doppler) between returning echo signals from one or more targets but also distinguish amplitude differences between the one or more targets and lock the attention of the radar onto a selected echo signal and continue to monitor that specific target echo so long as that target is of particular interest as determined by the radar system, and (2) a target persistence and environment filter for such devices for preventing the radar device from giving false alarms due to brief target echoes resulting from birds or wayside objects.
2. Description of Related Art
U.S. Pat. No. 4,673,937 issued to John W. Davis on Jun. 16, 1987 and assigned to the Assignee of the present invention teaches a vehicle borne radar system presently believed to be at the leading edge of the vehicle borne radar art.
However, the above-referenced radar system is not able to distinguish one individual target echo signal from a plurality of incoming target echo signals of approximately the same amplitude and lock on to that particular target echo signal until that target echo signal is replaced by a new particular target echo signal.
There is a continuing need to improve the safety of highway vehicles operation for preventing impact with moving and stationary objects and to safely increase the density of vehicles traveling the world's roadways by monitoring the distance, speed and direction of travel between one vehicle following another thereon to conserve available road space by safely increasing the number of vehicles on a given roadway at any given time and yet maintain a higher than now possible degree of safety for the passengers carried by those vehicles.
The present invention relates to an improved vehicle borne radar system for monitoring possible dangerous conditions for a particular vehicle traveling on a vehicle roadway. More particularly, the present invention relates to an improved vehicle borne radar system having a target persistence and environment filter for preventing the radar system from giving false alarms due to short duration target echoes resulting from birds or wayside objects.
It is also known, as shown for example by U.S. Pat. No. 3,952,303 of Watanabe et al, to transmit and receive at three different frequencies on a time division basis, with two of the frequencies being used to determine range, closing speed and likelihood of collision and the third frequency being combined with one of the first two to determine direction. However, three frequency systems are capable of even further simplification in the circuitry thereof using different techniques of determining the desired information. Moreover, the transmit and receive frames containing the frequencies can be wasteful in that only small portions thereof are needed to receive and segregate the signals of different frequency, with the remaining portions being unused.